New research is proving that COVID-19 is mainly transmitted in enclosed indoor spaces — even when you’re six feet apart and wearing masks.
Since the start of the COVID-19 pandemic, experts have been largely divided on the primary mode of transmission of its causative virus. On the one hand, the World Health Organization (WHO) was adamant about COVID-19 being transmitted through droplets exhaled from an infected person’s nose and mouth, which would then drop to the ground and no longer be able to reach another person situated six feet away. The “six-foot rule” became influential in informing policies such as social distancing, and closures of facilities such as schools, businesses, transportation options like jeepneys, and others where there was not enough space for people to socially distance. On the other hand, there are scientists who have said that the coronavirus can be transmitted through the air.
The WHO would later on adapt this, but not in its entirety. According to them, airborne infection could only occur in hospital settings, where infected aerosols could remain suspended in the air. However, a few months later, in July 2020, they pivoted, saying transmission inside indoor locations that are “inadequately ventilated” and where people spend a “prolonged period of time” could no longer be ruled out.
At present, scientists are finding ways to better communicate that COVID-19 is airborne. They are also measuring transmission of the virus inside enclosed spaces. As it turns out, airborne transmission has been responsible for large quantities of infections and has possibly become its primary vector. This means that a lot of the policies that have been in place may no longer be valid, and there is a need to revisit them.
One study that supports this idea is a three-time peer-reviewed article by two Massachusetts Institute of Technology (MIT) professors: Martin Z. Bazant, who teaches applied mathematics and chemical engineering, and John W.M. Bush, who teaches applied mathematics. Entitled “A guideline to limit indoor airborne transmission of COVID-19”, it appears in the journal Proceedings of the National Academy of Sciences of the United States of America (PNAS) and features a formula that measures airborne transmission in indoor spaces. It operates on the premise that airborne transmissions are causing the spikes in coronavirus cases globally.
Bazant and Bush used evidence obtained from various cases considered as “superspreading events”, such as the Skagit Chorale practice in Washington, where 53 out of 61 people present were infected; the Ningho bus journey that resulted to 23 infections; occurrences in high-rise buildings in Korea that are linked by air ducts; hospital room cases where respiratory aerosols from COVID-19 patients were present; and over 7,300 individual cases in China.
Based on the analysis of Bazant and Bush, the commonalities between these cases were the following: (1) several individuals who contracted the virus were located more than six feet away from an infected individual; (2) the spaces they were in were enclosed or did not have adequate ventilation and (3) infected individuals stayed in those spaces for prolonged periods of time. Bazant and Bush used these to come up with their formula for risk of infection, which also considered air filtration and circulation, immunization, variant strains, mask use, and respiratory activities within the space such as breathing, eating, speaking, and singing.
“The importance of airborne transmission of COVID-19 is now widely recognized,” Bazant and Bush wrote in their study. “While tools for risk assessment have recently been developed, no safety guideline has been proposed to protect against it.”
Why This Matters
As COVID-19 cases continue to surge in many countries, these considerations can be used as a springboard for revising the current guidelines to include greater focus on infections that may occur in indoor spaces. The new Bazant and Bush formula can also be used to calculate how certain factors can either increase or decrease risk of infection.
Another key result of the study is that it debunks the widely believed and followed six-foot rule for social distancing. According to the study, it doesn’t matter how far away you are from an infected person. What matters more is how much time you spend with that person, how much ventilation there is in the room you are in, and if there are activities that heighten your risk.
Beyond its implications for the scientific and medical communities, the study has the potential to influence key areas of the world’s response against the pandemic, such as lockdowns, business closures, and resource allocation for medical facilities.
For example, it implies that mask wearing is still important because it can prevent transmission through large droplets from sneezes and coughs and through direct plumes of air, but it may no longer be necessary when an individual is outdoors in a non-densely populated area. Bazant and Bush claim that even in large outdoor crowds, mask wearing may no longer be necessary if individuals are spaced at least three feet apart, as outdoor air tends to sweep away infectious airborne droplets.
Contact tracing protocols, which presently classify a close contact as someone who is within six feet of an infected individual for at least 15 minutes, will also have to be revisited. Because of airborne transmission, anybody in an enclosed space, even one who is six feet away or more and wearing a mask, is considered a close contact and will need to be tested. These current measures become less significant if the virus is airborne as infected air can circulate inside a room and seep through masks.
The study also highlights the importance of isolating infected individuals and cleaning infected indoor air. Those who are staying at home with somebody who tested positive should pay attention to ventilation and air circulation. Workers who go to offices, which are typically air-conditioned and enclosed, as well as their other close contacts, should also be tested regularly.
The findings of the study also mean that enclosed spaces such as restaurants, offices, and buses should consider keeping their windows open and installing fans to keep the air moving. Outdoor dining will also be the safest way to conduct businesses for food establishments, while classrooms that are 12 feet high with 900 square feet of floor space, and with natural or mechanical ventilation can be used by about 20 students for an extended period of time as long as the room is quiet, resting respiration is the norm, and extended physical activities are limited or none at all. Vaccinating students will further lower the risk.
The birth of new and more transmissible variants of COVID-19 also means that ventilation should be increased while time spent indoors, as well as crowd capacity, should be decreased to offset risk. On the other hand, spaces and means of transportation with great ventilation are allowable, as they pose significantly less risk.
As for medical facilities, it is important that they receive adequate support to combat the onslaught of the pandemic. COVID-19 may not be as infectious as other airborne diseases like measles, but the increase in the number of people spending time in indoor spaces matched with inadequate contact tracing and localized testing measures will surely devastate an already overworked healthcare system. We have seen this in the recent rise of infections, which took place after the economy gradually reopened. Committing the same mistakes puts people in danger.
At the individual level, we have to pay attention to the spaces we are in and what we do in those spaces. Are we indoors or outdoors? Are there enough windows and fans? How much time are we spending inside? Is anyone shouting, singing, or releasing droplets through coughing or sneezing? Those who have the means, may also purchase devices that measure carbon dioxide within a room. In this way, it will be possible to quantify respiration levels and raise awareness of risk.
The greater calamity that could ensue will be dependent on whether we adapt this paradigm shift or not, as the airborne nature of the virus upends many of the policies that are currently in place.
Bazant and Bush’s study, in addition to many others, solidifies evidence that airborne transmission in enclosed indoor spaces is behind the increase inCOVID-19 infections, and public health officials must make the necessary policy revisions. For one, there is a more urgent need to regulate use of enclosed indoor spaces like offices and restaurants, not limited to strict enforcement of social distancing and mask wearing protocols. Bazant and Bush may have come up with a formula for calculating risk of infection, but coming up with country-specific solutions and ensuring public safety is a responsibility that lies in the hands of the health ministries of country governments.